Modern aseismic design of structural steel buildings (particularly high-rise structures) provides for an analysis under dynamic loading, but the actual construction involves a statically connected structure. Much of the energy absorption (necessary in earthquake design) takes place in the yield zone of the material from which the frame members (columns and beams) of the building are formed. This yielding usually represents permanent deformation of the structural frame members and very often the permanent deformation is of such magnitude to have either destroyed the usefulness of the building or created the need for very expensive repair of the building. The reason for this is that, within the elastic limit of steel, the usual material of structural members, the area of the stress-strain hysteresis curve (FIG. 1) is very small. The curve defines deformation with respect to load as load is applied, and recovery to original shape and location as the load is removed.
The area of the hysteresis curve of FIG. 1 represents energy absorbed rather than energy stored. It is only when the steel material of structural frame members is worked in its yield zone that it absorbs energy, but it does not recover to its original shape because the yielding is permanent.
What is needed to accompany modern dynamic design of buildings of structural steel or other structural metal is modern dynamic connections for the numerous structural frame members of such a building, such connections being of the type which not only have shock-absorbing capabilities but also are capable of permitting structural frame members interconnected thereby to be in face-to-face contact with each other and to slide over each other so that energy tending to deform the structural frame members will be dissipated as heat generated by frictional effects. The material of such connections should be resilient so that the structural frame members will have a very "fat" hysteresis curve as shown in FIG. 2; thus, the building will recover not only its original size, shape and location but also will have absorbed energy in the connections and will have dissipated energy as heat of friction without subjecting the building frame as a whole to permanent damage due to extreme deformation.